1. Field of the Invention
An aspect of the invention generally relates to a trellis encoding device for trellis-encoding a transmission stream for digital broadcasting and a method thereof. More particularly, an aspect of the invention relates to a trellis encoding device and method in a transmission system for generating and transmitting a transmission stream into which a supplementary reference signal is inserted for trellis-encoding the transmission stream and correcting parity errors caused by initializing memories of a trellis encoder block to a known state before trellis-encoding the supplementary reference signal in the transmission system to improve a reception performance of an Advanced Television Systems Committee (ATSC) Vestigial VSB Digital Television (DTV) system that is an American-type digital terrestrial broadcasting system.
2. Description of the Related Art
An ATSC VSB DTV system that is an American-type digital terrestrial broadcasting system is a single-carrier system, and provides a field sync for each unit of 312 data segments. Accordingly, this system exhibits poor reception performance over an inferior channel, particularly over a Doppler fading channel.
FIG. 1 is a block diagram of an example of a transmitter and a receiver of an American-type digital terrestrial broadcasting system complying with an ATSC Enhanced VSB (EVSB) DTV standard that has been proposed by Philips Electronics. This system generates and transmits a dual transmission stream by adding a robust stream to a normal stream of the conventional ATSC VSB system. A robust stream is a stream that has been subjected to a robust data process to provide improved reception performance compared to a normal stream over an inferior channel, particularly over a Doppler fading channel. The current version of this standard is ATSC Digital Television Standard A/53, Revision E, dated Dec. 27, 2005, with Amendment No. 1, dated Apr. 18, 2006, and can be downloaded from www.atsc.org. This standard is referred to hereafter as ATSC Standard A/53E. The contents of this standard are incorporated herein by reference in their entirety.
As shown in FIG. 1, the digital broadcasting transmitter includes a randomizer 11 randomizing a dual transmission stream, a Reed-Solomon (RS) encoder 12 which is a concatenated coder adding parity bytes to the dual transmission stream to correct errors occurring due to channel characteristics during transmission, an interleaver 13 interleaving the RS-encoded data according to a specified interleaving pattern, and a ⅔ rate trellis encoder 14 mapping the interleaved data into 8-level symbols by performing a ⅔ rate trellis-encoding of the interleaved data. The dual transmission stream received by the randomizer 11 is an MPEG-2 transmission stream, and thus the digital broadcasting transmitter of FIG. 1 performs an error correction coding of the MPEG-2 transmission stream. The digital broadcasting transmitter of FIG. 1 is an 8-VSB system because the trellis encoder 14 maps the interleaved data into 8-level data symbols.
The digital broadcasting transmitter of FIG. 1 further includes a multiplexer (MUX) 15 multiplexing a field sync signal and a segment sync signal with the data symbols from the trellis encoder 14 to obtain an ATSC VSB DTV data frame having the configuration shown in FIG. 2, and a VSB modulator 16 inserting a pilot into the data symbols that have been multiplexed with the field sync signal and the segment sync signal by adding a specified DC value to the data symbols, performing a VSB modulation of the data symbols by pulse-shaping the data symbols to obtain a VSB-modulated signal, and up-converting the VSB-modulated signal to an RF channel band signal which is then transmitted over a channel.
Accordingly, in the digital broadcasting transmitter of FIG. 1, a multiplexer (not shown) multiplexes the normal stream and the robust stream to obtain a dual transmission stream to be transmitted over one channel, and inputs the dual transmission stream to the randomizer 11. The input data is randomized by the randomizer 11, the randomized data is outer-coded by the RS encoder 12 serving as an outer coder, and the outer-coded data is interleaved by the interleaver 13 according to a specified interleaving pattern. The interleaved data is inner-coded in units of 12 symbols and mapped into 8-level symbols by the trellis encoder 14. A field sync signal and a segment sync signal are multiplexed with the data symbols from the trellis encoder 14 by the multiplexer 15. A pilot is inserted in the data symbols that have been multiplexed with the field sync signal and the segment sync signal by the multiplexer 15, the data symbols with the inserted pilot are VSB-modulated by the VSB modulator 16 to obtain a VSB-modulated signal, and the VSB-modulated signal is up-converted to an RF channel band signal which is then transmitted over the channel.
The digital broadcasting receiver of FIG. 1 includes a tuner (not shown) down-converting the RF channel band signal received through the channel to a baseband signal, a VSB demodulator 21 performing sync detection and demodulation on the baseband signal, an equalizer 22 compensating the demodulated signal for channel distortions such as multipath, a Viterbi decoder 23 correcting errors in the equalized signal to obtain data symbols and decoding the data symbols to obtain decoded data, a deinterleaver 24 deinterleaving the decoded data according to the specified interleaving pattern used by the interleaver 13 of the digital broadcasting transmitter, a RS decoder 25 correcting errors in the decoded data, and a derandomizer 26 derandomizing the error-corrected data from the RS decoder 25 and outputting an MPEG-2 dual transmission stream.
Hence, the digital broadcasting receiver of FIG. 1 recovers the original signal inputted to the randomizer 11 of the digital broadcasting transmitter of FIG. 1 by reversing the operations performed by the digital broadcasting transmitter of FIG. 1 by down-converting the RF channel band signal to the baseband signal, demodulating and equalizing the baseband signal, and performing a channel decoding operation on the baseband signal.
FIG. 2 shows an ATSC VSB DTV data frame having the having the field sync signal and the segment sync signal that is used in the American-type digital terrestrial broadcasting system. As shown in FIG. 2, one frame consists of two fields, and one field consists of one field sync segment as the first segment, and 312 data segments. In the ATSC VSB DTV data frame, one data segment corresponds to one MPEG-2 packet, and consists of a 4-symbol segment sync signal and 828 data symbols.
The segment sync signal and the field sync signal shown in FIG. 2 are used for synchronization and equalization in the VSB demodulator 21 and the equalizer 22 in the digital broadcasting receiver of FIG. 1. That is, the field sync signal and the segment sync signal are known data known to both the digital broadcasting transmitter and the digital broadcasting receiver of FIG. 1, which is used as a reference signal for the equalization performed by the equalizer 220 in the digital broadcasting receiver of FIG. 1.
As discussed above, the digital terrestrial broadcasting system of FIG. 1 generates and transmits a dual transmission stream by multiplexing the robust stream with the normal stream of the conventional ATSC VSB DTV system so that the robust stream is transmitted together with the conventional normal stream.
However, the digital terrestrial broadcasting system of FIG. 1 cannot enhance the poor reception performance of the conventional normal stream over a multipath channel even when the dual transmission stream with the multiplexed robust stream is transmitted. That is, the reception performance for the normal stream is not enhanced at all even when the dual transmission stream is transmitted. In addition, the reception performance for the turbo stream over the multipath channel does not show any great improvement.
A technique of inserting a supplementary reference signal into the dual transmission stream to enhance the reception performance of the turbo stream is under development. Accordingly, a technique of properly encoding the dual transmission stream having the inserted supplementary reference signal is required.